A semiconductor device that has a volatile memory and a nonvolatile memory mixed in one chip has been developed. The volatile memory is fast in operation speed but requires a refresh operation. In contrast, the nonvolatile memory is slow in operation speed but requires no refresh operation.
In recent years, a semiconductor memory device has been developed which has a nonvolatile memory cell area and a volatile memory cell area provided in a memory cell array making use of a difference in memory cell characteristics. In this semiconductor memory device, a cell in the volatile memory cell area is weak in, for example, data retention, whereas a cell in the nonvolatile memory cell area is strong in, for example, data retention. In the semiconductor memory device, a volatile memory cell area and a nonvolatile memory cell area have been set before shipping. Therefore, it has been difficult to change the areas arbitrarily